U.S. patent application number 12/447549 was filed with the patent office on 2010-01-07 for pulse width modulation control for heat pump fan to eliminate cold blow.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100000239 12/447549 |
Document ID | / |
Family ID | 39536591 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000239 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
January 7, 2010 |
PULSE WIDTH MODULATION CONTROL FOR HEAT PUMP FAN TO ELIMINATE COLD
BLOW
Abstract
A heat pump refrigerant system is provided with a pulse width
modulation control for a fan moving air over the indoor heat
exchanger. When it is determined that there is insufficient heat
rejected by the indoor heat exchanger to heat the volume of air
being delivered by the fan into the conditioned environment, the
volume of air supplied to the conditioned environment is reduced by
utilizing one of pulse width modulation techniques to cycle the
indoor fan motor to reduce the average volume of supplied air.
Therefore, a precise control over the temperature of air delivered
to the conditioned space is achieved, temperature of the delivered
air is increased to the target value, and so-called "cold blow"
conditions are avoided.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
39536591 |
Appl. No.: |
12/447549 |
Filed: |
December 21, 2006 |
PCT Filed: |
December 21, 2006 |
PCT NO: |
PCT/US06/48896 |
371 Date: |
April 28, 2009 |
Current U.S.
Class: |
62/89 ; 62/115;
62/186; 62/428; 62/498 |
Current CPC
Class: |
F25B 13/00 20130101;
F25B 2313/02741 20130101; F25B 2313/0293 20130101; F25B 2313/0314
20130101 |
Class at
Publication: |
62/89 ; 62/498;
62/428; 62/186; 62/115 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25B 1/00 20060101 F25B001/00; F25D 17/04 20060101
F25D017/04 |
Claims
1. A heat pump comprising: a compressor for compressing refrigerant
and delivering the refrigerant to a downstream indoor heat
exchanger, said indoor heat exchanger being provided with an
air-moving device for moving air over said indoor heat exchanger
and into an environment to be conditioned, refrigerant passing from
said indoor heat exchanger through an expansion device and then
through an outdoor heat exchanger, refrigerant from the outdoor
heat exchanger returning to the compressor; and a control for said
air-moving device for said indoor heat exchanger, said control
providing a pulse width modulation signal to adjust the
time-average volume of air moved by said air-moving device over
said indoor heat exchanger when it has been determined that there
is insufficient heat rejected by said indoor heat exchanger to heat
a nominal volume of air to a desired temperature.
2. The heat pump as set forth in claim 1, wherein a four-way valve
selectively routes refrigerant from said compressor to said indoor
heat exchanger when the heat pump is operating in a heating mode,
and to said outdoor heat exchanger when the heat pump is operating
in a cooling mode.
3. The heat pump as set forth in claim 1, wherein said air-moving
device is a fan.
4. The heat pump as set forth in claim 1, wherein a motor for said
air-moving device is a single-speed motor, and said pulse width
modulation control rapidly cycles the motor.
5. The heat pump as set forth in claim 4, wherein said pulse width
modulation control rapidly cycles the motor between an "on"
position and an "off" position.
6. The heat pump as set forth in claim 5, wherein a time interval
for said "on" position is determined by at least one of temperature
requirements and efficiency considerations.
7. The heat pump as set forth in claim 1, wherein a motor for said
air-moving device is a two-speed motor, and said pulse width
modulation control rapidly cycles the two-speed motor between at
least one of a higher speed and a lower speed, the lower speed and
the "off" position and the higher speed and the "off" position.
8. The heat pump as set forth in claim 7, wherein the time interval
at each speed position is determined by at least one of temperature
requirements and efficiency considerations.
9. The heat pump as set forth in claim 1, wherein a motor for said
air-moving device is a multi-speed motor, and said pulse width
modulation control rapidly cycles the multi-speed motor between
multiple speeds, including the motor "off" position.
10. The heat pump as set forth in claim 9, wherein the time
interval at each speed position is determined by at least one of
temperature requirements and efficiency considerations.
11. The heat pump as set forth in claim 1, wherein the environment
to be conditioned is provided with a temperature sensor for sensing
the temperature of air being delivered into the environment, and
said sensed temperature being provided to said control, such that
said control can adjust the time-average volume of air moved into
the environment by utilizing said pulse width modulation technique
to match the sensed temperature to a desired temperature.
12. The heat pump as set forth in claim 1, wherein said indoor heat
exchanger is a condenser, while said heat pump operates in a
subcritical region at least for a portion of the time.
13. The heat pump as set forth in claim 1, wherein said indoor heat
exchanger is a gas cooler, while said heat pump operates in a
transcritical region at least for a portion of the time.
14. The heat pump as set forth in claim 1, wherein the pulse width
modulation cycling rate is determined by at least one of the
air-moving device reliability requirements, the temperature
variation tolerance band requirements and efficiency
considerations.
15. The heat pump as set forth in claim 1, wherein the pulse width
modulation control cycles said air-moving device between at or near
zero speed and a non-zero speed, and the consequent cycle starts
while the air-moving device is still in motion.
16. A method of operating a heat pump comprising the steps of: (1)
compressing refrigerant and delivering the refrigerant to a
downstream indoor heat exchanger, indoor heat exchanger being
provided with an air-moving device moving air over said indoor heat
exchanger and into an environment to be conditioned, refrigerant
passing from said indoor heat exchanger through an expansion device
and then through an outdoor heat exchanger, refrigerant from the
outdoor heat exchanger returning to the compressor; and (2)
controlling said air-moving device for said indoor heat exchanger,
by providing a pulse width modulation signal to adjust the
time-average volume of air moved by said air-moving device over
said indoor heat exchanger when it has been determined that there
is insufficient heat rejected by said indoor heat exchanger to heat
a nominal volume of air to a desired temperature.
17. The method as set forth in claim 16, wherein a four-way valve
selectively routes refrigerant from said compressor to said indoor
heat exchanger when the heat pump is operating in a heating mode,
and to said outdoor heat exchanger when the heat pump is operating
in a cooling mode.
18. The method as set forth in claim 16, wherein said air-moving
device is a fan.
19. The method as set forth in claim 16, wherein a motor for said
air-moving device is a single-speed motor, and said pulse width
modulation control rapidly cycles the motor.
20. The method as set forth in claim 19, wherein said pulse width
modulation control rapidly cycles the motor between an "on" and an
"off" position.
21. The method as set forth in claim 20, wherein a time interval
for said "on" position is determined by at least one of temperature
requirements and efficiency considerations.
22. The method as set forth in claim 16, wherein a motor for said
air-moving device is a two-speed motor, and said pulse width
modulation control rapidly cycles the two-speed motor between at
least one of a higher speed and a lower speed, the lower speed and
the "off" position and the higher speed and the "off" position.
23. The method as set forth in claim 22, wherein the time interval
at each speed position is determined by at least one of temperature
requirements and efficiency considerations.
24. The method as set forth in claim 16, wherein a motor for said
air-moving device is a multi-speed motor, and said pulse width
modulation control rapidly cycles the multi-speed motor between
multiple speeds, including the motor "off" position.
25. The method as set forth in claim 24, wherein the time interval
at each speed position is determined by at least one of temperature
requirements and efficiency considerations.
26. The method as set forth in claim 16, wherein the environment to
be conditioned is provided with a temperature sensor for sensing
the temperature of air being delivered into the environment, and
said sensed temperature being provided to said control, such that
said control can adjust the time-average volume of air moved into
the environment by utilizing said pulse width modulation technique
to match the sensed temperature to a desired temperature.
27. The method as set forth in claim 16, wherein said indoor heat
exchanger is a condenser, while said heat pump operates in a
subcritical region at least for a portion of the time.
28. The method as set forth in claim 16, wherein said indoor heat
exchanger is a gas cooler, while said heat pump operates in a
transcritical region at least for a portion of the time.
29. The method as set forth in claim 16, wherein the pulse width
modulation cycling rate is determined by at least one of the
air-moving device reliability requirements, the temperature
variation tolerance band requirements and efficiency
considerations.
30. The method as set forth in claim 16, wherein the pulse width
modulation control cycles said air-moving device between at or near
zero speed and non-zero speed, and the consequent cycle starts
while the air-moving device is still in motion.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a heat pump, wherein a fan for
moving air into a conditioned environment is provided with a pulse
width modulation control to address the problem of "cold blow".
[0002] Heat pumps are known in the art and utilized to provide
cooling to a conditioned environment during time periods of hot
weather or excessive internal thermal load generation, and to
provide heat to the same indoor environment when the weather is
cold. Also, there are known a more simplistic heat pump designs
that are able to operate just in a heating mode. Heat pumps have
great potential to provide efficient conditioning to the indoor
environment, however, there have been impediments to their use.
[0003] One known problem with existing heat pump designs is
so-called "cold blow." "Cold blow" occurs when the heat pump does
not have sufficient heat rejection capability to adequately heat
air being driven into the environment to be conditioned.
[0004] When this phenomenon occurs, air driven over the indoor heat
exchanger and into the environment to be conditioned is not heated
to the temperature desired by the occupant of the environment,
causing uncomfortable conditions to the occupant, that is of course
undesirable.
[0005] It has been known to address "cold blow" by reducing the
volume of air delivered into the environment to be conditioned
either through the use of a variable speed drive, or through a
two-speed fan motor. A two-speed fan motor does not provide
sufficient flexibility to adequately tailor the airflow to achieve
the desired temperature. A variable speed drive may provide such
flexibility, however, it is quite expensive, represent an
additional source of potential reliability problems and associated
with efficiency losses. Thus, there has not been an adequate cost
effective solution offered to resolve this problem.
[0006] Pulse width modulation controls are known for controlling
the amount of refrigerant passing to a compressor in a refrigerant
system, such as an air conditioning system or a heat pump. However,
pulse width modulation controls have not been utilized to address
the "cold blow" problem mentioned above.
SUMMARY OF THE INVENTION
[0007] In a disclosed embodiment of this invention, fan moving air
over an indoor heat exchanger is operated in a pulse width
modulated manner. The use of the pulse width modulation control
precisely tailors the amount of air moved over the indoor heat
exchanger and into the climate-controlled environment, such that
the heat rejected by the indoor heat exchanger, in the heating mode
of operation, to the indoor air stream is sufficient to heat the
controlled volume of air to the desired temperature. Thus, if less
heat is rejected by the indoor heat exchanger and available to heat
the air, the amount of air being driven into the environment will
be reduced accordingly, such that air is delivered to a
climate-controlled environment at the target temperature.
[0008] By closely controlling and cycling the fan between "on" and
"off" positions, in single-speed fan applications, the present
invention is able to precisely control the temperature of air
delivered to the indoor space. If a two-speed fan is utilized, the
pulse width modulation control can cycle the fan between the lower
and a higher speed to achieve the desired effect. In the tatter
case, the cycling between a lower speed and zero speed as well as a
higher speed and zero speed is also permissible, if desired.
[0009] The time interval during which the fan is engaged in a
full-speed position, for a single-speed fan, or in a higher speed
position, for a two-speed fan, is determined by the temperature
requirement and comfort level, while the cycle rate is primarily
determined by fan assembly reliability requirements and temperature
variation tolerance bounds. Further, frequent cycling is not
necessary, since refrigerant system thermal inertia compensates for
sudden changes in fan speed. Also, the fan does not have to be
brought to a full stop state, between activation and deactivation
of the pulse width modulation signal, since the mechanical inertia
allows for a softer start in a subsequent cycle.
[0010] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a schematic of a heat pump incorporating the
present invention.
[0012] FIG. 2 shows a cycling sequence for a single-speed fan.
[0013] FIG. 2 shows a cycling sequence for a two-speed fan.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] A refrigerant system 20 is illustrated in FIG. 1 and
includes a compressor 22 delivering a refrigerant to a discharge
line 23, and through a four-way valve 24 (if a heat pump is
dedicated to heating applications only, then a four-way valve is
not required) to an indoor heat exchanger 26. Downstream of the
indoor heat exchanger 26, the refrigerant passes through an
expansion device 28, and then to an outdoor heat exchanger 30. The
outdoor heat exchanger 30 is provided with a fan 32 to move air
over the external heat transfer surfaces of the outdoor heat
exchanger 30. Downstream of the outdoor heat exchanger 30, the
refrigerant passes again through the four-way valve 24, and into a
suction line 33 returning the refrigerant to the compressor 22. The
refrigerant system 20 is illustrated in FIG. 1 in a heating mode of
operation. The refrigerant system 20 can be moved to an air
conditioning cooling mode of operation by switching the four-valve
24 and routing the refrigerant from the discharge line 23 initially
to the outdoor heat exchanger 30, through the expansion device 28,
and returning the refrigerant from the indoor heat exchanger 26 to
the suction line 33. However, the present invention is directed to
an improvement that is particularly applicable when the refrigerant
system is in a heating mode of operation. The FIG. 1 schematic for
the heat pump 20 is a basic schematic, and as known to a person
ordinarily skilled in the art, can be improved by adding a number
of enhancement features and various options. All these designs are
within the scope and can benefit from the invention.
[0015] As shown in FIG. 1, an air-moving device, such as fan 34,
moves air over the indoor heat exchanger 26 and into an environment
to be conditioned 36. In the heating mode of operation, the heat
exchanger 26 performs a condenser (or a gas cooler, for
transcritical applications) function. At times (for instance, at
lower ambient temperatures or at high heating load demands in the
conditioned space), there may be insufficient heat rejection
capacity provided by the heat exchanger 26 to adequately heat a
nominal volume of air driven by the fan 34 over external heat
transfer surfaces of the heat exchanger 26 and into the indoor
environment 36. In such situations, the indoor air stream does not
reach the desired temperature creating uncomfortable so-called
"cold blow" conditions for an occupant of the indoor environment
36. A control 38 (that could be a stand-alone control or a
refrigerant system control) is provided with a feedback
communication loop from a temperature sensor 49 and is capable to
operate the indoor fan 34 in a pulse width modulation mode.
Therefore, the control 38 can detect a lower than desired
temperature of the air being delivered into the indoor environment
36. In such cases, the control 38 is operable to provide a pulse
width modulation control to a motor for the indoor fan 34 such that
the average volume of air supplied by the indoor fan 34 to the
conditioned environment 36 is reduced. As the average volume of air
is sufficiently reduced the heat rejected by the indoor heat
exchanger 26 is sufficient enough to heat that reduced volume of
air to a temperature desired by an occupant of the conditioned
environment 36. As known, the desired temperature may be set by a
thermostat 50. Alternatively, the thermostat 50 can be utilized as
a feed back device for the control 38.
[0016] By utilizing the pulse width modulation control, a
single-speed motor for the indoor fan 34 is rapidly cycled between
"on" and "off" (or fully engaged and fully disengaged) positions.
In the case of a two-speed fan, the indoor fan motor may be rapidly
cycled between its higher and lower speed positions, as well as
between the lower speed position and an "off" position and between
the higher speed position and an "off" position". In either case,
the volume of air delivered into the environment 36 is precisely
adjusted, such that the heat rejected by the indoor heat exchanger
26 is adequate to heat this adjusted air volume to the desired
temperature. As mentioned above, when a multi-speed fan motor is
used, the pulse width modulation cycling can be executed between
any of the speeds, including a speed of zero.
[0017] It is proposed to control the indoor fan 34, in the heating
mode of operation, by pulse width modulation method to precisely
adjust the temperature of the conditioned (heated) air delivered to
the indoor environment 36. This control is straightforward and does
not require additional components. The cycling frequency is
determined by the indoor fan assembly reliability and temperature
variation tolerance requirements. The time interval at each speed
position is defined by the required air temperature values and
comfort level to be achieved and efficiency considerations.
Frequent cycling will not be necessary and is avoided, since
refrigerant system thermal inertia smoothes sharp variation of
operational parameters and compensates for sudden abrupt peeks and
valleys. Cycling can be executed between a zero and-full speed, for
a single-speed fan, and between the lower and the higher speed
positions, as well as between the lower speed position and an "off"
position and between the higher speed position and an "off"
position", for a dual-fan speed fan. Multi-speed fans provide even
a higher degree of flexibility and precision control. Lastly,
indoor fan mechanical inertia may assist in continuous rotation of
the indoor fan (although at a constantly reducing speed), while the
pulse width modulation signal is activated and deactivated allowing
for a softer start in a subsequent cycle.
[0018] FIG. 2 is an exemplary chart of a temperature of air
supplied to the conditioned space versus time, for a refrigerant
system wherein the indoor fan motor is operable at a single, full
speed, in an "on" or fully engaged position, and at a zero speed,
in an "off" or fully disengaged position. As can be seen,
initially, the indoor heat exchanger is not capable to provide
sufficient amount of heat to the nominal volume of air supplied to
the conditioned environment, and the actual temperature is below
the desired temperature, promoting "cold blow" conditions. Also, as
can be seen, when the pulse width modulation control for the indoor
fan is engaged, the indoor fan motor begins to cycle between a full
speed (or an "on" position) and a zero speed (or an "off"
position), reducing the time-average amount of air supplied to the
conditioned environment. As a result, the actual supply air
temperature, increases, as well as approaches and reaches the
desired temperature, while the pulse width modulation cycle
parameters are adjusted to the correct values.
[0019] Similarly, FIG. 3 shows another embodiment, wherein the fan
motor is operable at two speeds and can be cycled by the pulse
width modulation control between the higher and lower speed
positions, as well as between the lower speed position and an "off"
position and between the higher speed position and an "off"
position". As an example, here, the fan is cycled between the lower
speed position and the higher speed position. Again, the actual
supply air temperature increases and soon approaches the desired
temperature, with this arrangement.
[0020] It has to be noted that although a square waveform is used
in FIGS. 2 and 3 embodiments for the pulse width modulation
control, other waveforms are also feasible and within the scope of
the invention. For instance, a trapezoidal, a triangular, a rounded
square or any other waveform can be utilized instead.
[0021] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
* * * * *